This invention is a new type of differential gear. Differential gears are well known and are typically found in automobiles, buses, riding lawnmowers and other land type vehicles. There was a time when the typical differential gear did not function satisfactorily if one wheel of a vehicle lost traction and the other did not. Because the wheel with traction stopped turning and the wheel without traction continued to turn, just the opposite of what was desired. Prior art differential gears are designed so that one half axle and bevel gear turns faster than the opposite slower turning half axle and bevel gear so as to accommodate the vehicle turning a corner. Recently, there have been marketed two designs of a differential gear employing the one way action of a worm gear to limit such slippage, in other words a limited slip gear.
In these two recent designs, as with most any other differential gear, the power of the engine is transferred to a differential housing via a ring gear. One of these new differential gear designs, see Popular Science, February, 1984, Pages 58-61, which uses a pair of worm wheels (from two to three pairs, depending on the size of the differential) mounted on the differential housing to turn the worm gears splined to an axle shaft. One worm wheel of each pair turns the left axle shaft and the other worm wheel turns the right axle shaft.
Because the worm wheel cannot turn the worm gear, it locks on the gear and turns the axle shaft, propelling the vehicle forward during non-turning travel. The right and left axle shafts (in right and left wheels) turn simultaneously. Each wheel then rotates at the same speed. When a vehicle makes a turn, each wheel rotates at a slightly different RPM. For example, during a left turn, the left wheel will slow down by two RPM's and the right wheel will speed up by two RPM's. One axle shaft always slows down at the exact rate that the other speeds up. This difference in RPM is transferred to the worm wheels because the worm wheels on the axle shaft can turn the worm wheel and equalize the other side via a 1:1 spur gears, which act as balancing gears. Thus, the engine is "locked" or engaged on the axle shaft while allowing for differential action when negotiating turns
The differential gear of the instant invention is more simple in construction. It does not have a worm gear; it has a cage delimiting a space in which two juxtaposed colinear rotatable cylinders are disposed. In each cylinder, there is an elliptically shaped groove and in each groove there are two spheres. The cage is so constructed so that each sphere is in contact not only with each rotatable cylinder, but also with the cage as well. Part of a given sphere is partly in an eliptical groove of one rotatable cylinder and partly in the eliptical groove of the other rotatable cylinder. Each sphere remains in such contact, as the rotatable cylinder is rotated, and travels the route delimited by the elliptical groove of a given rotatable cylinder. The elliptical path of the grooves and the two spheres perform the function of an endless worm gear and is the basis for the limited slip properties of this gear.